Dissertations / Theses on the topic 'Chemical aspects'

Chemical and biological processes present a challenge when it comes to modelling and analysis. The models usually have to take into account many chemicals and complex interactions and in turn, they are often described by large ODE systems with complicated nonlinear terms. If there is a lack of quantitative information about the chemical interactions, there will also be parameter uncertainty in the systems. Such systems present a challenge to analyse. In response, an increasing consensus calls for emphasis on the underlying chemical reaction network structure and the use of network information to predict possible system dynamics.

In order to demonstrate the ability of microbubble flotation to superclean coal to ash levels of less than 2%, several Eastern U. S. coals have been tested. The results show that the process is capable of producing superclean coal with improved recovery as compared to the conventional flotation process.

To further improve and understand the microbubble flotation process, electrokinetic studies of the hydrocarbon oils used in flotation as collectors have been conducted. Also, the effect of oil emulsifiers on the zeta potential of oil droplets has been studied. In general, oil droplets are negatively charged and negative zeta potential is reduced with the addition of nonionic and cationic surfactants. On the other hand, the negative charge is increased with the addition of an anionic reagent. It has also been shown that the negative zeta potential of oil droplets increases with increasing hydrocarbon chain length.

The effects of different collectors on induction time and flotation have been determined by conducting microflotation and induction time experiments using an Elkhorn seam coal sample. The results show that industrial oils combined with the coal have the shortest induction times and, therefore, the highest flotation yields as compared to pure hydrocarbon oils. It has also been shown that oil emulsifiers tend to increase flotation yield and reduce particle/bubble induction time.

Master of Science

Two open wet oxidation methods are described for the digestion of selected seafoods prior to total mercury determination using a cold vapour atomic absorption spectrophotometric technique. The first employs two acids (i.e. HNO3 and H2SO4) and two oxidants (i.e. KMnO4 and K2S2O8), and is suitable for use with a Perkin-Elmer Mercury Analysis System (MAS) and a Perkin-Elmer Mercury Analyzer 50A (MA). Excellent recoveries were obtained for mussel samples spiked with various quantities of inorganic mercury [Hg(N03)2]. For the optimum part of the calibration curve of the MAS (0.1–0.7 μg/ml Hg), the percentage recovery (%R) fluctuated between 98.26 and 101.98. The limit of detection (LOD) was calculated to be 18.7 ng of mercury per sample analysed and sensitivity of 0.011 μg of mercury was obtained. Results for fish samples determined with both units showed excellent agreement and precision (RSD = 3.23 -4.25). However, the MA was found inadequate for the determination of the low mercury levels encountered with the mussel samples. It was shown that a desiccant assembly must be installed whenever samples with low mercury content are analysed, i.e. less than 0.5 μg per sample digested.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
This work describes the phytochemical investigation of Hamelia patens (Rubiaceae) native from Guaramiranga montain, CearÃ, Brazil. Sucessive chromatographic treatment of the ethanol extract of leaves led to the isolation of the pentaciclic oxindole alkaloids pteropodine, isopteropodine, palmirine, and the new isopalmirine, besides the flavonoid kaempferol l-3-α-O-rhamnopyranosyl-(1-6)-β-D-galactopyranoside. The study of the ethanol extract of the stems led to the isolation of the steroids β-sitosterol and stigmasterol as mixture, stigmast-4-en-3,6-dione, and the triterpene ursolic acid. The ethanol extract of the trunk yielded vanillic acid and the β-sitosterol and stigmasterol glucosilated. The isolation of the chemical constituents were performed by the use of chromatographic techniques, including flash cromatography, thin layer crohromatography, preparative crhomatography, and preparative high performance liquid chromatography (HPLC). The strucutral charactherization were performed by the use of infrared, mass spectrometry and nuclear magnetic resonance, including one (1H NMR, 13C NMR and DEPT 135) and two-bidimensional pulse sequences (HMBC, HSQC, COSY e NOESY), and comparison with literature data.
Neste trabalho foi realizado a investigaÃÃo fitoquÃmica de Hamelia patens (Rubiaceae) nativa da Serra de Guaramiranga-CE. A realizaÃÃo de sucessivos tratamentos cromatogrÃficos a partir do extrato etanÃlico das folhas possibilitou o isolamento dos alcalÃides oxindÃlicos pentacÃclicos pteropodina, isopteropodina e palmirina, jà citados na literatura para a espÃcie, do alcalÃide isopalmirina de carÃter inÃdito na literatura, alÃm do flavonÃide canferol-3-O-α-L-rhamnopiranosil-(1→6)-β-D-galactopiranosÃdeo. O estudo do extrato etanÃlico dos talos possibilitou o isolamento dos esterÃides β-sitosterol e estigmasterol como mistura, do estigmast-4-en-3,6-diona, alÃm do triterpeno Ãcido ursÃlico. A partir do extrato etanÃlico do caule foram obtidos o Ãcido vanÃlico e a mistura de esterÃides β-sitosterol e estigmasterol glicosilados. Para o isolamento dos metabÃlitos secundÃrios foram empregadas tÃcnicas cromatogrÃficas convencionais como cromatografia em camada delgada, cromatografia filtrante, cromatografia flash, cromatografia preparativa e Cromatografia LÃquida de Alta EficiÃncia (CLAE). A caracterizaÃÃo estrutural dos compostos isolados foi realizada atravÃs de tÃcnicas espectroscÃpicas como infravermelho, espectrometria de massas e ressonÃncia magnÃtica nuclear, incluindo tÃcnicas uni (RMN 1H e RMN 13C e DEPT 135) e bidimensionais (HMBC, HSQC, COSY e NOESY), alÃm de comparaÃÃo com dados descritos na literatura.

The formulation of an aqueous paint involves the mixing of a very complex chemical system. The objective of this study was to investigate the colloidal and surface properties of this type of system. From this an overall picture of the physico-chemical interactions occurring between the pigment and polymer, and the effect of the soluble components, could be obtained. By a greater appreciation of the basic chemistry of the paint system, improvements of the final commercial products cculd be possible. A simple paint system was designed which contained industrial pigment, poly(vinylacetate) polymer and soluble ccnstituents including sodium hexametaphosphate (dispersant), and sodium dodecylsulphate (emulsifier). A non ionic thickener, sodium hydroxyethylcellulose, and an ionic thickener, carboxymethyl cellulose was also included. The effect of the alumina coating was investigated by testing both alumina coated pigment, RTC90, uncoated ccnventional rutile, RD rutile and alumina pigment, Hydral. The effect of these soluble aluminium species on the pclymer was also demonstrated. The interaction of the soluble components on the polymer and pigment WoS investigated using microelectrophoresis and adsorption techniques. The distribution of mcbilities in colloidal samples was obtained for both coated and uncoated pigments in a variety of solutes. The effect of thickener concentration on paint formulations and millbases was measured at constant temperature in precision bore glass columns. The data was analysed using an interactive computer programme based on the work of Carstensen & Su (1970a 1970b). The effect of thickener with respect to flocculation, film formation and gloss was also estimated using optical and infrared techniques. This study has given an idea of the complexity of paint formulations and the need for further model studies on the individual components of the system.

Fused glass beads as a sample preparation method for X-ray Fluorescence spectroscopy (XRF) were introduced in 1957 by Claisse; it soon became the preferred method to introduce oxide samples to the spectrometer, because heterogeneity, mineralogical and particle size effects are eliminated during the fusion process. Matrix effects are largely reduced by the resulting dilution. With the recent advances in XRF spectrometers, instruments with enhanced generator and temperature stability, improved sensitivity (even for light elements), and effective matrix correction software are available. Consequently, the largest proportion of analytical error results from the sample preparation step. Sampling error will always contribute the largest overall error but that is not the topic of this discussion. After more than 50 years of fused bead use in XRF analysis, certain matrices remain problematic. Although many fusion methods for chromite-, sulphide- and cassiterite-rich materials have been published, easily reproduced, routine methods for these still elude analytical chemists. Lengthy fusions at temperatures higher than 1100ºC are often prescribed for refractory materials and ores, and until recently one of the biggest challenges was a metal-bearing sample e.g. contained in slags or certain refractory materials. This study was conducted to identify and elucidate the reactions occurring in the formation of a lithium borate glass, but also between the lithium borate and oxides during glass formation. Different analytical techniques were used to investigate the reactions occurring during the fusion process based on theoretical glass-making principles. As a starting point, Thermo Gravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) were used jointly to evaluate the reactions occurring during the fusion of lithium borate glasses, and at a later stage, oxide/flux mixtures. When a different TGA instrument was used, Differential Scanning Calorimetry (DSC) was used in conjunction with the TGA. Observed reactions were modelled in a muffle furnace to produce identical material in larger quantities, and this material was then investigated using X-ray Powder Diffractometry (XRD), Raman Spectroscopy and Electron Microprobe Analysis (EPMA). The most enlightening result from the TGA/DSC results was the large mass loss above 1050 ºC. Literature often prescribes prolonged fusions at elevated temperatures for certain fusions, but it was proved beyond reasonable doubt that this practise causes volatilisation of the flux and leads to erroneous analytical results. The next analytical technique applied to the flux and flux/oxide samples was XRD. Where pre-fused fluxes were investigated, the XRD data served as confirmation of the glassy state of the pre-fused flux as a broad humpy scan indicative of an amorphous material was seen in stead of a diffractogram with sharp, well defined peaks. After heating to above the temperature of re-crystallisation, the phases present could be identified from the diffractogram. Provisional results using the in-situ, high temperature stage point towards the possibility of using this technique to great effect to investigate the presence of different phases formed at high temperatures. Flux-oxide mixtures were measured on the high temperature stage and after cooling a new phase was observed indicating that new phases formed during a fusion reaction. As the heating stage is slow-cooled, the chance of crystallisation in the glass is good, providing the possibility for investigating this formation of new phases at elevated temperatures further with a more suitable heating element that will contain the material. Raman spectroscopy was subsequently used to gain information about the bonds within the flux. Pure lithium tetraborate and lithium metaborate fluxes were analysed as well as flux oxide mixtures. The vibrations could not be predicted from first principles as band broadening occurs in glasses that makes theoretical predictions very difficult. The data obtained was compared to similar studies in literature and good agreement was found. In oxide-flux mixtures definite new bands were observed that was not part of the flux or oxide spectrum. EPMA results allowed calculation of the maximum solubilities of an oxide in a specific flux. It was done using Cr2O3 and ZrO2 and compared well with experimental values obtained from literature. The microscope images revealed some new insights into the theory of XRF fusions. It could clearly be seen that dissociation of the minerals in the sample occurred, thus proving that no mineralogical effects exist in a fused glass bead, and it could be observed that the flux oxide mixture devitrify when over saturated.
Dissertation (MSc)--University of Pretoria, 2010.
Chemistry
unrestricted

This PhD Thesis deals with the study of marine natural products as candidates in either drug discovery and development. In particular, the investigation focused on benthic organisms, i.e. those fixed or in a close relation with the sea bottom. These organisms, many of which are sessile or slow-moving invertebrates, thus unable to escape quickly from their predators, and devoid of physical protection (shell or hard texture), have developed alternative protective strategies as well as the production of chemical weapons. Compounds involved in the chemical defence, besides the ecological function, can display interesting pharmacological activities. Organisms of different phyla (Algae, Molluscs and Cnidarians) and from diverse geographical areas (Mediterranean Sea and China) were investigated. The benthic diatom Cocconeis scutellum is able to affect the sex reversal in the protandric shrimp Hippolyte inermis, inducing apoptosis (programmed cell death) in the crustacean's androgenic gland. Thus, we wondered whether these diatoms could act also in other crustaceans and on human cancer cells, in order to evaluate their applications in aquaculture and medicine. In fact, some commercially important crustaceans show a bimodal pattern of growth, in which males grow faster and are bigger than females. For this reason, the production of all-male populations is more advantageous. The administration of proapoptotic compounds in an early larval phase could be a method to manipulate the sex in these crustaceans. Nevertheless, our study demonstrated that diatom compounds did not induce apoptosis in the androgenic gland of other species, suggesting a targeted and specific action of C. scutellum metabolites. On the other hand, the biological assays on human cancer cell lines showed that solid tumours were more responsive to C. scutellum than haematological tumours and normal cells, suggesting a specific toxic action of the diatom compounds. In addition, we demonstrated that the most active fraction to induce apoptosis in cancer cells was that containing the highest amount of eicosapentaenoic acid (EPA), described in the literature for its anticancer and proapoptotic properties. This fraction detained the cell cycle at G2/M phase and the results in terms of apoptosis and reduced cell viability produced by this fraction were comparable with those induced by EPA. Western blotting experiments showed that diatoms triggered apoptosis by the extrinsic pathway, i.e. by means of activation of caspase 8, and confirmed the involvement of effector caspase 3. In addition, C. scutellum was studied for the first time from the chemical point of view. By GC-MC we identified more than 100 compounds, mainly fatty acids, sterols and glycerides, and excluded the presence of short chain aldehydes.
In collaboration with the University of Athens, the chemical study on the anaspidean mollusc Aplysia fasciata was carried out. From its digestive and hermaphroditic glands 16 metabolites were isolated by a combination of chromatographic techniques, and they were identified by spectroscopic analysis. Six of them (6-hydroxy-1-brasilene, epibrasilenol acetate, (3Z,9Z)-7-chloro-6-hydroxy-12-oxopentadeca-3,9-dien-1-yne, 6-epi-beta-snyderol, 16-acetoxy-15-bromo-7-hydroxy-9(11)-parguerene), belonging to different classes of sesquiterpene, acetogenin and diterpene compounds, are new and related with metabolites isolated from different species of the red alga Laurencia, the animal's diet.
In the Istituto di Chimica Biomolecolare (Italy), the chemical and biological investigation on the Chinese soft coral Sinularia sp. was performed. We isolated four new casbene compounds, i.e. bicyclic diterpenes characterized by a cyclopropane fused with a 14-membered macrocycle, which are usually found in Euphorbiaceae plants and rarely in marine organisms. Contrastingly to most natural cis ring-fused casbenes, in Sinularia co-existed cis and trans compounds and this suggested a non-stereospecific biosynthetic mechanism. The 4 casbenes were active against Gram+ bacteria and just casbene 3 also against Gram- bacteria, only hydroxylated casbenes displayed anti-feeding properties, and they did not exhibit antiproliferative activity.
"Metabolitos secundarios de organismos bentónicos: aspectos ecológicos y químicos"

Depositada por Michela Nappo

TEXTO:

El objetivo de esta Tesis es el estudio de los productos naturales marinos y su posible relevancia en el desarrollo de nuevos medicamentos. La investigación se enfocó sobre los organismos bentónicos, i.e. los que viven en contacto con el fondo marino y que, a pesar de la falta de protección física y la escasa movilidad de la mayoría de las especies, han desarrollado mecanismos de defensa alternativos, como la producción de armas químicas. Estos compuestos, dotados de propiedades ecológicas, a menudo exhiben también importantes actividades farmacológicas. Se consideraron organismos pertenecientes a diferentes phyla (algas, moluscos y cnidarios) y áreas geográficas. Las diatomeas Cocconeis scutellum afectan la reversión sexual del decápodo proterándrico Hippolyte inermis, induciendo apoptosis (muerte celular programada) en la glándula androgénica del crustáceo. En esta Tesis evaluamos también la capacidad de dichas diatomeas en afectar el cambio de sexo de otros crustáceos, en particular los de interés comercial, y de actuar sobre las células tumorales humanas, a fin de encontrar posibles aplicaciones en acuicultura y medicina. También se valoró el patrón metabólico de las diatomeas mediante cromatografía de gases/espectrometría de masas, identificando más de 100 compuestos (ácidos grasos, esteroles y glicéridos), no constatándose la presencia de aldéhidos de cadena corta.
En la Universidad de Atenas, se realizó el estudio químico del molusco anaspídeo Aplysia fasciata. Mediante diferentes técnicas cromatográficas y espectroscópicas, se aislaron 16 metabolitos, de los cuales seis eran nuevos (6-hidroxi-1-brasileno, epibrasilenol acetato, (3Z,9Z)-7-cloro-6-hidroxi-12-oxopentadeca-3,9-dien-1-ino, 6-epi-beta-snyderol, 16-acetoxi-15-bromo-7-hidroxi-9(11)-parguereno), relacionados con metabolitos de algas rojas del género Laurencia, que constituyen la dieta del animal.
En el Instituto de Química Biomolecular (Pozzuoli, Italia) se realizó tanto el estudio químico como los experimentos biológicos con el coral blando Sinularia sp. procedente de China. De esta especie se aislaron 4 nuevos compuestos casbénicos (diterpenos bicíclicos formados por un anillo ciclopropánico fusionado a un macrociclo de 14 átomos) cuya estructura es frecuente en plantas de la familia Euphorbiaceae y bastante más rara en los organismos marinos. Los casbenos hidroxilados eran repelentes alimenticios; todos son activos frente a las bacterias Gram+ y sólo el casbeno 3 es también activo frente a las bacterias Gram- .

This thesis presents three different topics in phosphorus-containing heterocycles. The first topic is about novel phosphorus-containing flame-retardants to be used in poly-urethane foams. The background and importance of flame-retardants is discussed as well as the synthesis and testing data of compounds that were expected to have good flame-retardant properties. More importantly, these compounds represent a class of flame-retardants that can be chemically incorporated into the polymer, which will overcome current negative aspects such as leaching and fogging. The test results show that the tested compounds perform about as well as commercially available materials and that there are indications that they are chemically incorporated into the polymer. The second topic is about the cytotoxic effects of aziridines. The phosphate moiety of a DNA-chain can act as a nucleophile that ring-opens an aziridine. This reaction results in the formation of a phosphate triester with a potential nucleophile, namely an amino group, in a beta-position. These two factors make the hydrolysis of the DNA chain at this particular point much more likely. A model study was designed to investigate the likelihood of DNA-chain cleavage by aziridines as these form an important class of anti-tumour agents. From this model study it can be concluded that the cytotoxic effects of aziridines have to be contributed to alkylation of other nucleophilic sites at DNA than to strand cleavage preceded by alkylation of the phosphate backbone. The last topic covers a stereochemical investigation of the metal catalysed hydrolysis of a cyclic nucleotide. It presents the first stereochemical assignment of the metal catalysed hydrolysis of a phosphate ester. In line with most enzyme catalysed hydrolyses of phosphate esters the reaction investigated here was assigned to go with inversion of configuration.

My Ph. D. work is about theoretical basis and applications of density functional theory (DFT). DFT has demonstrated a good balance between computing costand accuracy, so it has become one of the most popular daily-used quantum chemistry methods. The first part of my work is about the asymptotic behavior of finite-system wave-functions. The exponential decaying asymptotic behavior is confirmed andthe structure of the prefactors is further explored. By comparing the asymptotic behavior of the Dyson orbitals and the Kohn-Sham orbitals, we have also provided a physical interpretation of the Kohn-Sham orbital energies. Then we want to rebut the theory of "unconventional density variation" proposed more than 20 years ago. Supported by theoretical analysis and numericalevidence, we proved that all density variations are the same in nature. We have also extended two total energy functionals suggested before to the Hartree-Fock method. Numerical tests on different molecules show these functionals are very promising in accelerating the SCF convergence of quantum chemistry calculations. Finally, we completed a comprehensive theoretical study on the tautomers of pyridinethiones. Many molecular properties predicted from theory are comparedwith those got from experiments. The dominant forms of the tautomers are confirmed to be the thione forms. This demonstrates the power of DFT methods, and this work can serve as a reference for studying similar molecules.

A study has been made on the mechanism of rosin sizing in papermaking. By using microelectrophoresis and laboratory prepared handsheets, a study of the effect of pH, certain metal salts, and various physical parameters on the overall electrokinetics and sizing efficiency of the system has been made. By the use of a novel sizing method it was possible to effectively size handsheets in the alkaline pH range, which had previously not been possible when using rosin dispersion sizes. This permitted the inclusion of calcium carbonate as a filler, which has particular advantages in the finished paper. Use of the theory proposed by Derjaguin-Landau-Verwey and Overbeek on colloidal interaction, made it possible to explain and predict the likely outcome of sizing experiments, by analysing the electrokinetics of the system components. A comparative study on the effect of rosin fortification and the stabilisation of the dispersions by the use of casein has been made. From the results obtained, fortification leads to an improvement in sizing, particularly if the drying of the paper is not very efficient. Whereas the interactions of casein primarily effect the stabilisation of the dispersion, protein desorption from the solid-liquid interface causes initial flocculation of the dispersion. If the desorption is kept to a minimum, the dispersion is still stable and an effective sizing agent.

Adverse drug reactions (ADRs) are a major obstacle for the development of new medicines. They are also a leading cause of patient morbidity and mortality. Although ADRs affect many different organs and bodily systems, drug induced liver injury has lead to the withdrawal of several drugs at the post licensing stage, and is a key cause of drug attrition. Many of the drugs that cause liver injury are thought to do so through metabolism to a reactive metabolite, exposure to which can cause modification of cellular proteins, leading to loss of function, and can result in a loss of cellular homoeostasis. It is therefore important to understand the chemistry and the downstream biochemical events associated with bioactivation. Information on the chemistry of metabolism coupled with mechanistic biomarkers reflective of certain pathways of hepatic injury would enable both researchers and physicians to predict and diagnose DILI, leading to the improvement of safe drug design. This thesis focuses firstly on the use of in vitro models and mass spectrometry to provide integrated data on the metabolism and toxicity of xenobiotics, using thiophene containing molecules as a paradigm. The thiophene ring has the potential to be bioactivated via S-oxidation and epoxidation pathways, and several thiophene containing drugs have been associated with drug induced liver injury. The investigations described intended firstly to elucidate the chemistry of methapyrilene bioactivation using mass spectrometry and hydrogen-deuterium exchange. The following two chapters aimed to establish a link between bioactivation and toxicity of thiophenes and to evaluate two in vitro models as tool for predicting DILI. The final experimental chapter aims to investigate the potential of ophthalmic acid (OA) to act as a serum biomarker reflective of depletion of hepatic levels of the protective tripeptide, glutathione (GSH). Disturbance of GSH levels through quenching of reactive metabolites can lead to disturbance of its anabolism and catabolism pathways. Indeed, serum OA levels, a GSH analog, have been shown to rise following hepatic GSH depletion. This work utilises GSH adduct formation as a marker of bioactivation of thiophenes in several different in vitro models. Rat liver microsomal incubations were analysed using hydrogen deuterium exchange and LC-MS to define the reactive metabolite of methapyrilene as an S-oxide of the thiophene ring. Freshly isolated rat hepatocytes or single P450 expressing THLE cell cultures were exposed to either methapyrilene, tienilic acid, ticlopidine or 2-phenylthiophene and subsequent LC-MS analysis confirmed GSH adduct formation for all compounds in the isolated rat hepatocyte model, but only for 2-phenylthiophene in the THLE cell model. Cytotoxicity was also investigated in both models, and all compounds were found to cause a greater degree of toxicity in the isolated rat hepatocyte molecule than in the THLE model. By exposing rodents to depletors of hepatic GSH, such as acetaminophen and diethylmaleate, and monitoring the resultant serum OA levels, it has been determined that OA is not a reliable mechanistic marker of hepatic GSH depletion. Kinetic studies of OA in rat serum have revealed that OA is subject to a similar metabolic and elimination pathway as GSH. The overall scope of this work reveals the usefulness of LC-MS/MS to determine S-oxide and epoxide adducts in in vitro studies. The freshly isolated rat hepatocyte model was a useful tool for providing integrated metabolic and toxicological data of thiophene containing molecules and has the potential to be expanded to include data on covalent binding and levels of DILI biomarkers. The single CYP expressing THLE cell model was not as useful in this case, but has been used in other studies to explore the role of discrete P450 enzymes in toxicity and metabolism. Whilst it is unfortunate that serum OA did not reflect hepatic OA in such a way that it could be easily exploited as a biomarker, this does help us to understand that the plethora of potential biomarkers uncovered by proteomic, metabolomic and transcriptomic studies need to be investigated in depth in order to understand their applications across different species and systems.

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 211-233).
Electrodeposition is a fascinating electrochemical phenomenon that contains deep physical insights and has broad practical applications. At the heart of the physics governing electrodeposition is a competition between a destabilizing force caused by surface crests growing more rapidly than surface troughs in a positive feedback loop and a stabilizing force arising from surface energy effects that prevent the surface from roughening excessively. The physical manifestation of this surface instability is the formation and propagation of dendrites. Some applications of electrodeposition include electroplating of metals such as copper and charging of next-generation high-energy-density metal batteries such as lithium metal batteries. From both theoretical and practical standpoints, it is important to understand how to control and exploit electrode-position.
In this thesis, we explore electrodeposition in a homogenized charged porous medium that contains a fixed background charge density, which affords us a new knob for controlling electrodeposition. In practice, such a background charge density can either naturally arise from ionization of surface functional groups or be generated through experimental techniques such as layer-by-layer deposition of polyelectrolytes on the pore surfaces. We investigate the theoretical aspects of electrodeposition in charged porous media in three different ways. First, we introduce a simple transport model that accounts for the background charge density and couple it with electrochemical reaction kinetics for electrodeposition. We then validate the coupled model by comparing predicted steady state current-voltage relations and linear sweep voltammetry with experimental data for copper electrodeposition in a variety of nanoporous media.
Second, we perform linear stability analysis on the model to understand how key system parameters such as the background charge density affect the linear stability of the metal surface. We then show good agreement between theoretical predictions and experimental observations of the critical and instability wavelengths for copper electrodeposition in cellulose nitrate membranes. Third, we carry out impedance analysis on the model and explain some intriguing features in the experimental impedance spectra for copper electrodeposition in anodic aluminum oxide membranes. Through these three different types of analysis, we demonstrate the predictive power and robustness of the theory despite its simplicity
by Edwin Sze Lun Khoo.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemical Engineering

During the last decades, the interest in corrosion of metals and alloys from an environmental and health perspective has increased rapidly as a consequence of stricter environmental and human exposure legislations, their extensive use as implant materials and an increasing understanding related to occupational and/or daily exposure to airborne particles. Corrosion-induced metal release, however, needs to be understood in detail and to include knowledge related to chemical speciation, i.e. the oxidation state, complexation and chemical form of released metals, parameters of high importance when considering toxicity. In this licentiate work, corrosion-induced metal runoff from roofing materials (copper, zinc, and chromium(III)-, and chromium(VI) surface treated galvanized steel) has been investigated from an environmental perspective with focus on chemical speciation of released metals (Papers I-II). From these papers it was evident that the total concentration measured in the runoff water is not sufficient for any environmental risk assessment. The environmental fate including changes in chemical speciation and hence metal precipitation has to be considered. For example, it was shown that the copper concentration decreased by three orders of magnitude already in the internal drainage system of a shopping centre with a copper roof, to a concentration lower than storm water collected from a nearby parking space (Paper I). Also, speciation measurements can explain corrosion, metal release and surface processes of chromium surface treated galvanized steel at different sites (urban and marine). Any environmental risk assessment has to be done by considering all metal species released, and compared with ecotoxic values. For example, when most chromium(VI) (the most toxic species) was released, significantly less zinc was released at the same time which decreased the overall ecotoxicity of the runoff water significantly (Paper II). When assessing environmental risks by standard laboratory tests, it is important to understand all mechanisms which are possibly influenced by individual experimental parameters and which often are different for different test substances. Some metals released, as seen in the case of iron, may precipitate with time and be pH-, solution- and buffering dependent. This behavior can lead to strongly underestimated measured metal concentrations (Paper III). When particles of metals or alloys are to be investigated (Papers III-VI), it is essential to conduct a thorough particle characterization, since the surface properties cannot be defined. In addition, the surface properties (oxide layer properties) change with varying particle size (Paper VI) and with other experimental parameters such as dispersion (Paper VI). All iron-, and chromium-based particles investigated (Papers III-VI) revealed large differences between alloy particles and pure metals. Particles of pure iron and nickel released significantly more metals compared with particles of the investigated alloys, whereas particles of pure chromium released less metals compared with the alloys. Particles of stainless steel (AISI 316L), ferro-chromium and ferro-silicon-chromium released very low amounts of metals (Papers III-VI). The released quantity increased with increased acidity (Papers III-VI) and also in the presence of complexing agents (ongoing research). The manufacturing process is of high importance, as observed for stainless steel particles when compared with a side product from stainless steel production with similar composition that released significantly more metals (Paper III). Particles of metal oxides, i.e. chromium(III)oxide and iron(II,III)oxide, released very low amounts of metals due to their thermodynamic stability. Ongoing research activities focus on the specific influence of complexing agents and proteins on the metal release process from massive sheet and particles of metals and alloys. The applicability and the possibility to use different analytical tools are investigated and elaborated for small-sized particles. A detailed understanding of the correlation between material and particle characteristics, the metal release process, the chemical speciation in interaction with proteins and/or cells, and the particle/cell interaction is essential to enable any correlation between material/particle characteristics and toxicity. The aim of this licentiate summary is – in contrast to the six included scientific papers – to explain the importance of chemical speciation for corrosion processes from a health and environmental perspective in a popular way to reach a broad non-academic audience. The summary is hence written as a guidance document for stakeholders and the regulatory community working with environmental and health risk assessment.
QC 20101006

Chemical mechanical polishing (CMP) of metals has emerged as a critical process step for the fabrication of advanced integrated circuit devices in the semiconductor industry. In a typical metal CMP process, the metal film is blanket deposited to fill recessed features on a patterned dielectric on silicon. Following metal deposition and gap fill, the metal overabundance is polished away by CMP, leaving an inlayed metal pattern or damascene structure on the substrate. Removal of the metal overabundance also planarizes the wafer surface for subsequent processing steps. The material removal process occurring during CMP is thought to involve the combined action of chemical oxidation and dissolution, and mechanical removal of material by abrasives. However, the relative contribution of mechanical and chemical effects during metal CMP is not well understood. The objective of this research was to characterize the fundamental electrochemical behavior of tungsten and aluminum thin films in polishing chemistries of interest to CMP. It was also of interest to determine the extent to which electrochemical oxidation and dissolution, or mechanical removal by abrasive action assists in material removal during CMP. A simultaneous electrochemical tester and polishing tool was developed to characterize the electrochemical behavior of tungsten and aluminum during and after abrasion. Small-scale polishing experiments were also carried out to measure polishing (removal) rates of the metals during CMP. Electrochemical dissolution rates and polishing rates were compared. It was found that the electrochemical dissolution rate of tungsten or aluminum during or after abrasion was very small compared to actual polishing rates. However, the presence of an oxidant enhanced polishing rates dramatically. The findings indicate that the mechanism for removal during CMP is primarily corrosion assisted metal removal, and not electrochemical dissolution and/or removal of the oxidation product of the metal.

The chemical mechanical planarization (CMP) process is critical in fabricating ultra large scale integrated (ULSI) circuit devices in semiconductor industry. In a typical aluminum damascene interconnect scheme, Al is usually blanket deposited over a liner layer to fill contact holes and vias. After deposition, the excess of Al is removed by CMP, leaving Al only in the holes and vias to form interconnects. Since the slurries used for aluminum CMP typically contain an oxidant and other chemical additives, the electrochemical behavior of Al and the liner may be expected to affect the polishing rates. In addition, when the excess of Al is removed, a surface transition from Al to liner occurs. Since Al and the liner may exhibit different electrochemical behaviors in the slurry, galvanic coupling between Al and the underlayer is a possibility. Such a coupling may lead to localized corrosion or rate control problems. The objective of this research was to characterize the fundamental electrochemical behavior of thin aluminum-0.5%copper, titanium and aluminum/titanium stack films before, during and after abrasion in a commercially available alumina based slurry containing iodate as an oxidant. A special apparatus in which electrochemical tests can be carried out during polishing was fabricated and used for this research. It was found that the electrochemical corrosion rates during abrasion were much smaller than the actual polishing rates obtained with the simulated CMP apparatus, indicating that the mechanism of Al removal by the iodate based slurry may not be dominated by electrochemical factors. A sharp rise in corrosion potential (Ecorr) during the transition from Al to Ti film was measured during polishing of the Al/Ti film stack. This potential change during transition was of the order of 1V on the Al film deposited at room temperature. The transition was much sharper with the low-temperature (25°C) Al film than the high-temperature (475°C) Al thin film. The slower transition in OCP in high-temperature films is most likely due to a Ti-Al intermetallic compound formed at the Al/Ti interface. The galvanic corrosion between Al and Ti during polishing and Al post-polishing corrosion issues were also investigated. It was found that the galvanic corrosion rate between Al and Ti is 6*10⁻⁴ A/cm² and the corrosion potential is -0.24 V. Also, the corrosion current density for Al after abrasion and immersion in de-ionized water is lower than that in the slurry. In addition, the post polishing corrosion of Al in after abrasion in the iodate based alumina slurry was also investigated. It was found that the corrosion of Al in DI water after abrasion was insignificant.

Denna licensiatavhandling behandlar oxidativ upplösning av UO2. Upplösning av UO2 studeras huvudsakligen då UO2-matrisen hos använt kärnbränsle förväntas fungera som en barriär mot frigörande av radionuklider i ett framtida djupförvar. Lösligheten av U(IV) är mycket låg under i djupförvaret rådande förhållanden emedan U(VI) har betydligt högre löslighet. Oxidation av UO2-matrisen kommer därför att påverka dess löslighet och därmed dess funktion som barriär. I denna avhandling studeras den relativa effektiviteten av en- och två-elektronoxidanter för upplösning av UO2. Vid låga oxidantkoncentrationer är utbytet för upplösningen för en-elektronoxidanter signifikant lägre än för två-elektronoxidanter. För en-elektronoxidanter ökar dock utbytet med ökande oxidanthalt, vilket kan förklaras av den ökade sannolikheten för två konsekutiva en-elektronoxidationer av samma reaktionssite och den ökade möjligheten till disproportionering. Radikaler och molekylära radiolysprodukters relativa inverkan på oxidativ upplösning av UO2 studeras också i denna avhandling genom mätning av mängden upplöst U(VI) i γ-bestrålade system som dominerades av olika oxidanter. Dessa studier visade att upplösningshastigheten av UO2 kan uppskattas från oxidantkoncentrationer framtagna genom simuleringar av radiolys i motsvarande homogena system och hastighetskonstanterna för ytreaktionerna. Simuleringarna visar att de molekylära oxidanterna kommer vara de viktigaste oxidanterna i alla system i denna studie vid långa bestrålningstider (>10 timmar). Vid liknande simuleringar av α-bestrålade system fanns att vid förhållanden relevanta för ett djupförvar för använt kärnbränsle, är det endast de molekylära oxidanterna (i huvudsak H2O2) som är av betydelse för upplösningen av bränslematrisen. Då använt kärnbränsle innehåller en mängd radionuklider som utsätter UO2-matrisen för kontinuerlig bestrålning, är det av vikt att undersöka hur bestrålning påverkar reaktiviteten av UO2. Bestrålningseffekten på reaktionen mellan UO2 och MnO4- studerades. Dessa försök visade att bestrålning av UO2 vid doser >40 kGy leder till att reaktiviteten ökar upp till 1.3 gånger reaktiviteten av obestrålad UO2. Den ökade reaktiviteten kvarstår efter bestrålningen och effekten kan därför möjligen tillskrivas permanenta förändringar i materialet. Vid uppskattning av reaktiviteten hos använt kärnbränsle måste hänsyn tas till denna effekt då bränslet redan efter ett par dagar i reaktor blivit utsatt för doser >40 kGy. Det har tidigare föreslagits att hastigheten för en heterogen västka/fast-fas reaktion är beroende av partikelstorleken hos det fasta materialet, vilket har studerats för UO2-partiklar i denna avhandling. Experimentellt bestämda kinetiska parametrar jämförs med de föreslagna ekvationerna för fyra storleksfraktioner av UO2-pulver och en UO2-pellet. Studien visade partikelstorleksberoendet av andra ordningens hastighetskonstant och aktiveringsenergin för oxidation av UO2 med MnO4- beskrivs relativt väl av de föreslagna ekvationerna.
The general subject of this thesis is oxidative dissolution of UO2. The dissolution of UO2 is mainly investigated because of the importance of the UO2 matrix of spent nuclear fuel as a barrier against radionuclide release in a future deep repository. U(IV) is extremely insoluble under the reducing conditions prevalent in a deep repository, whereas U(VI) is more soluble. Hence, oxidation of the UO2-matrix will affect its solubility and thereby its function as a barrier. In this thesis the relative efficiency of one- and two electron oxidants in dissolving UO2 is studied. The oxidative dissolution yield of UO2 was found to differ between one- and two-electron oxidants. At low oxidant concentrations the dissolution yields for one-electron oxidants are significantly lower than for two-electron oxidants. However, the dissolution yield for one-electron oxidants increases with increasing oxidant concentration, which could be rationalized by the increased probability for two consecutive one-electron oxidations at the same site and the increased possibility for disproportionation. Furthermore, the relative impact of radical and molecular radiolysis products on oxidative dissolution of UO2 is investigated. Experiments were performed where the amount of dissolved U(VI) was measured in γ-irradiated systems dominated by different oxidants. We have found that the UO2 dissolution rate in systems exposed to γ-irradiation can be estimated from oxidant concentrations derived from simulations of radiolysis in the corresponding homogeneous systems and rate constants for the surface reactions. These simulations show that for all systems studied in this work, the molecular oxidants will be the most important oxidants for long irradiation times (>10 hours). Similar simulations of α-irradiated systems show that in systems relevant for a deep repository for spent nuclear fuel, only the molecular oxidants (mainly H2O2) are of importance for the dissolution of the fuel matrix. The effect on UO2 reactivity by irradiation of the material is of importance when predicting the spent fuel dissolution rate since the fuel, due to its content of radionuclides, is exposed to continuous self-irradiation. The effect of irradiation on the reaction between solid UO2 and MnO4- in aqueous solutions was studied. It was found that irradiation of UO2 at doses >40 kGy increases the reactivity of the material up to ~1.3 times the reactivity of unirradiated UO2. The increased reactivity remains after the irradiation and can possibly be attributed to permanent changes in the material. This issue must be taken into account when predicting the reactivity of spent nuclear fuel since the fuel is exposed to doses >40 kGy after only a few days in the reactor. It has earlier been suggested that the rate of a heterogeneous liquid-solid reaction depends on the size of the solid particles. This was investigated for UO2 particles in this thesis. Experimental kinetic parameters are compared to the previously proposed equations for UO2 powder of four size fractions and a UO2 pellet. We have found that the particle size dependence of the second order rate constant and activation energy for oxidation of UO2 by MnO4- is described quite well by the proposed equations.
QC 20101123

Various agents such as heat, ultrasound, rhodamine derivatives and carbonylcyanide m-chlorophenylhydrazone are used to induce cellular damage so as to understand certain events leading to cell death using a mammalian cell culture system - HeLa S3 cells. Clonogenic assay is insensitive as it is an end-point technique for determining the effectiveness of cell-killing. A combined approach using protein synthesis, oxygen consumption, time-sequenced morphological study, flow cytometric analysis and others is used instead. Ultrasound is used also because it can produce heat especially when focussing beams are employed. However, with the present experimental set-up system, it is the formation of microbubbles (cavitations) together with microstreaming in a fluid medium and not heat, that produce the 'shattering' damage to the HeLa S3 cells in suspensions. Heating e.g. at 42oC for a brief period can produce 'thermoprotection' to other stimuli, in this case ultrasound. Mitochondria are found to be highly sensitive to heat especially at 45oC and the compounds used in this study. Multivesicular and myelinoid-multivesicular bodies are related to mitochondria. Lysosomes do not appear to play a critical role in the early events leading to cell death. It is suggested that by damaging mitochondria leading to an irreversible state of cellular 'energy crisis' could be the earliest event in cell death.

Chemical looping combustion (CLC) is a promising fossil fuel combustion technology, which is able to separate CO2 from the flue gases without a large consumption of energy. In this thesis, the study was extended to look at the use of chemical looping materials within traditional fluidised bed combustion and investigation of the interaction between the fuel, the supplied air and the chemical looping agent. Three topics of chemical looping combustion are discussed, including 1) the Sherwood number in the fluidised bed; 2) properties of different oxygen carriers, Fe2O3 and CuO (with supporting materials), were tested in the fluidised bed reactor; 3) the simulation of a steady state and a dynamic model of a coal-fired CLC power plant using Fe2O3 as oxygen carriers. The Sherwood number, which represents the mass transfer rate, is important in the calculation of CLC process. With Sherwood number, the mass transfer rate kg around the acting particle can be calculated using correlation Sh=kg∙d/D, where d is the diameter of acting particle, and D is the diffusivity around the acting particle. Hayhurst and Parmar (Hayhurst and Parmar 2002) calculated the Sherwood number in the fluidised bed by using the CO/CO2 ratio, which was measured by the temperature difference between the carbon particle and the bulk phase (Hayhurst and Parmar 1998). However, the temperature of the particle could be overestimated, so the CO/CO2 ratio could be underestimated. In this thesis, a universal exhaust gas oxygen (UEGO) sensor was employed, which could measure the actual carbon consumption rate in the fluidised bed by oxidizing CO in the sample gas into CO2 and. Fe particles of the same size of the char particle is used to measure the O2 consumption rate, and thus eliminate uncertainty in the Sherwood number. The CO/CO2 ratio was calculated by using the carbon consumption rate and the O2 consumption rate. In contrast to Hayhurst and Parmar (Hayhurst and Parmar 2002) who assumed CO2 was the main product, for this char the actual ratio of CO/CO2 was almost zero. The measurement here is in agreement with Arthur. This more accurate determination of CO/CO2 allows a better estimate of the mass transfer coefficient and leads to a correction of the Hayhurst and Parmar’s (Hayhurst and Parmar 2002) correlation by a factor of 1⁄2. Interestingly, very small fluidised beds have mass transfer coefficients which are about twice that expected in a large bed (owing to the very different flow and indeterminate flow pattern). This means the correlation of Hayhurst and Parmar (Hayhurst and Parmar 2002), by fortuitous coincidence works wells for beds with diameters < 30 mm., without the correction factor, should be ignored. In the fluidised bed in a typical CLC process, different fluidising material could have different influence on the reactions. Thus, it is worth discussing different kinds of fluidising materials. The char combustion in the fluidised bed was simulated by using inert (sand) and active (Fe2O3 or CuO) fluidising materials, and air as fluidising gas. The results indicated that 1) CO combustion in the boundary layer leads to smaller carbon consumption rate and larger oxygen consumption rate; 2) Using Fe2O3 particles as fluidising materials slows down the carbon consumption rate, since the diffusivity of CO2 is smaller than CO; 3) CuO particles slow down the carbon consumption rate at large Sherwood number (Sh=2 or 2.5). The influence of using CuO as fluidising material is further discussed experimentally by using low O2 fluidising gas. The results indicated that since the amount of CuO used in the experiment is small, when the O2 concentration in the bulk phase is lower than the equilibrium concentration, the O2 concentration in the bulk phase gradually decreases, and the O2 concentration in the bulk phase has large influence on the char particle combustion. A steady state model of a coal-fired CLC power plant was simulated. The aim of the model was to test the suitable operating conditions of the power plant, such as recycle rate of oxygen carriers, for the power plant design. In the steady state model, the power plant consists of a combustor and a steam cycle. Hambach lignite coal, Polish bituminous coal and natural gas were tested as fuels. The results indicated that: (1) The effect of the fuel is largely due to the amount of oxygen required per GJ released; (2) Preheating is important, but seems to have a minor effect since the most of the heat is released at temperatures well above the pinch point; (3) since the temperatures of heat source in this research is well above the pinch point, all heat are usable for the steam cycle. In this case, the steam cycle and the chemical looping plant could be optimised separately; (4) As long as the preheat temperature of the air flow into the air reactor is higher than the temperature of turbines, in most of cases the power output is unaffected by the choice of variables, leaving the designer free to choose the most convenient. With the conclusions above, a dynamic model of a coal-fired CLC power plant using Fe2O3 as oxygen carrier is then simulated. The aims of this simulation include: 1) explaining the kinetics of Fe2O3 oxygen carriers at high temperature (1223K) in a fluidised bed reactor using Brown’s data (Brown 2010); 2) a 1GWth dynamic power plant was simulated to test different cases including changing power supply and power storage. In the dynamic model, a chemical looping power plant using Hambach lignite char is tested, and the parameters of the system are adjusted so as to simulate the operations of a real chemical looping power plant. The two-phase model is employed for the fluidised bed reactors. Experimental data from Brown (Brown 2010) was simulated using this model first to test its validity. Then the model is scaled up to simulate a 1GWth dynamic power plant. The ideal operation conditions are found, and a char stripper is found helpful for carbon capture.

Thesis (MScEng)--University of Stellenbosch, 2001.
ENGLISH ABSTRACT: Ferrohydrostatic separation (FHS) of materials is a float and sink technique which utilizes ferrofluid exposed to a non-homogeneous magnetic field. The efficiency of material separation depends on numerous variables. The most important variables, which were investigated individually, are the effects of moisture content, ferrofluid level, feedrate, particle size and material density distribution on separation efficiency. It is important to recover and recycle the ferrofluid attached to the products of separation so as to reduce the cost of the FHS technology and the amount of kerosene disposed of to the environment. This prompted research into some of the factors affecting ferrofluid recovery. The factors that were investigated are the effects ofFHS operation, material moisture content, particle size and porosity. The separation efficiency was found to be dependent on all the variables investigated. The effect of material moisture content is less pronounced for particles larger than 2.8 mm. This implies that wet feed material should be screened before ferrohydrostatic separation and material which particle size is less than 2.8 mm should preferably be treated dry. Wet material (less than 2.8 mm) floats, even though its density is greater than the cut-point density. This is owing to the immiscibility of the water coating the particles and the kerosene-based ferrofluid used for separation. It was found that the effect of ferrofluid level on separation efficiency is a function of both the density difference of the particles to be separated and the particle size. Separation efficiency as a function of ferrofluid level is poor for particles larger than 2 mm and is good when the density difference of the material to be separated is high, for instance between 2700 kg/nr' and 3530 kg/nr'. This shows that for efficient separation of coarse particles and near density material (material with density close to the cut-point density), the ferrofluid level should be controlled, preferably close to the maximum possible level. The effect of feedrate on separation efficiency is also a function of the densities of the particles to be separated. An increase in feedrate leads to poor separation for particles with densities close t~ each other. This implies that separation of near density material requires accurate feedrate control. It has been shown from simulation and modelling that the effective cutpoint density changes as the particle moves through the chamber until it eventually reaches its terminal velocity, given that the chamber is of sufficient size for this to occur. The effective cut-point density increases to the maximum as the particle enters the ferrofluid pool but settles down to a relative constant once the particle has reached its terminal velocity. The effective cut-point density was shown to decrease with an increase in particle magnetisation. It was found that this decrease in the cut-point density determines the density difference (difference between two particles) achievable when non-magnetic material is treated together with magnetic material. It is therefore important to magnetically scalp the feed material for efficient separation. When the material is not scalped, magnetic and nonmagnetic material with the same density might report to different density fractions, which leads to poor separation. This magnetic contribution to the effective density can be utilised in the separation of material with same density but different magnetisation. The efficiency offerrofluid recovery was found to be dependent on all the variables investigated. The amount of ferrofluid drawn from the FHS separator was found to decrease with an increase in the magnetic field. Furthermore, the amount of ferrofluid that remains attached to the particles after allowing ferrofluid to drain from the material is the same as that attached to the FHS products of separation at high magnetic fields. This shows that it is important to operate the ferrohydrostatic separator at high magnetic fields in order to attract most of the ferrofluid back to the separator. T-heamount of ferrofluid adsorbed onto and absorbed by the particles was found to decrease with an increase in the material moisture content. This is due to two factors. The first is that water occupies the vacant pores in the material. The second is that water forms a layer on the particle surface which is immiscible with kerosene-based ferrofluid. This phenomenon leads to a reduction in cost of the ferrohydrostatic separation technology when wet material as opposed to dry material is treated. As already described coarse material larger than 2.8 mm can be treated wet without detrimental effects on separation. For -8+4 mm particles, the ferrofluid loss ranges from 0.6 down to 0.14 kg/tonne of feed for 0 to 10 % material moisture content respectively. The amount of ferrofluid lost per tonne of feed was found to range from 0.73 to 0.56 kg for-O.85+O.5 mm to -12+8 mm particle sizes respectively. The increase in ferrofluid loss in small particles is due to the increase in surface area in small particles for ferrofluid adsorption. The increase in porosity increases the amount of ferrofluid lost due to the difficulties in recovering ferrofluid embedded in the pores of the particles. Adding water to coarse material lowers the amount of ferrofluid lost by reducing porosity. Modelling the amount of ferrofluid lost, as a function of particle size and porosity, would assist in determining the amount of ferrofluid required to treat a known amount of material. The quality of ferrofluid recovered was found to be the same as that initially used for material separation. This implies that the separation efficiency would not be affected by the use of recycled ferrofluid.
AFRIKAANSE OPSOMMING: Ferro-hidrostatiese skeiding van materiale is 'n flotasie (dryf) en besinkingstegniek wat gebruik maak van ferro-vloeistof wat blootgestel is aan 'n magnetiese veld. Die effektiwiteit van die materiaal skeiding is afhanklik van verskeie veranderlikes. Die belangrikste veranderlikes wat die skeidingseffektiwiteit beïnvloed is individueel bestudeer, naamlik voginhoud, ferro-vloeistof vlak, voertempo, partikelgrootte en materiaal digtheid verspreiding. Dit is belangrik om die ferro-vloeistof te herwin en te hergebruik om die koste van die proses en tegnologie te verminder en dus ook die hoeveelheid keroseen wat aan die omgewing blootgestel is. Dit het navorsing tot gevolg gehad oor die faktore wat ferro-vloeistofherwinning beïnvloed. Hierdie.faktore wat ondersoek is in hierdie studie is materiaal voginhoud, partikelgrootte en porositeit. Die skeidingseffektiwiteit was afhanklik van al die faktore wat ondersoek is. Die effek van materiaal voginhoud was minder beduidend vir partikels groter as 2.8 mm. Dit wys dat nat voermateriaal moet gesif word voor ferro-hidrostatiese skeiding, en materiaal met 'n partikelgrootte kleiner as 2.8 mm moet verkieslik gedroog word. Nat materiaal (minder as 2.8 mm) floteer selfs as die digtheid groter is as die snypunt digtheid. Dit is as gevolg van ondeurlaatbaarheid van die water wat die partikels bedek en die keroseen basis ferro-vloeistofwat gebruik word vir die skeiding. Dit is gevind dat die invloed op die skeidingseffektiwiteit van die ferrovloeistof vlak is 'n funksie van beide die digtheid van die partikels wat geskei word. Die partikelgrootte skeidingseffektiwiteit as 'n funksie van die ferro-vloeistof vlak, is swak vir partikels groter as 2 mm en is goed wanneer die digtheid verskil van die materiaal wat geskei moet word, hoog is, byvoorbeeld 2 700 kg/nr' en 3 530 kg/nr'. Dit wys dat vir die effektiewe skeidings vir groter partikels en naby digtheid materiaal (materiaal net 'n digtheid nabyaan die snypunt digtheid), moet die ferro- . vloeistofvlak baie goed beheer word, gewoonlik naby die maksimum vlak moontlik. Die effek van voertempo op die effektitiwiteit van skeiding is ook 'n funksie van die digtheid van die partikels wat geskei moet word. 'n Toename in die vloeitempo lei tot 'n swak skeiding van partikels met digthede wat naby mekaar lê. Dit wys weer daarop dat die skeiding van naby digtheid materiaal het die akkurate beheer van voertempo tot gevolg. Dit is gevind deur simulasie en modulering dat die effektiewe snypuntdigtheid verander soos die partikel deur die kamer beweeg totdat dit uiteindelik sy finale snelheid bereik (gegee dat die kamer groot genoeg is). Dit effektiewe snypunt digtheid verhoog tot 'n maksimum wanneer die partikel die ferro-vloeistof binne gaan, maar bereik na 'n kort tydperk 'n kostante waarde sodra die partikel sy finale snelheid bereik het. Die effektiewe snypunt digtheid verlaag met 'n toename in partikel magnetisme. Dit is gevind dat die afname in die snypunt digtheid bepaal die digtheidsverskil (verskil tussen twee partikels) wat bereikbaar is wanneer nie-magnetiese materiaal saam met magnetiese materiaal behandel word. Dit is dus belangrik om die voer materiaal magneties te skalpeer vir effektiewe skeiding. Wanneer die materiaal so behandel word, sal magnetiese en nie-magnetiese materiaal, met die dieselfde digthede, rapporteer in verskillende digtheidsfraksies wat sal lei tot swak skeiding. Die magnetiese bydrae tot die effektiewe digtheid kan gebruik word in die skeiding van materiaal met dieselfde digtheid, maar met verskillende magnetismes. Die effektiwiteit van ferro-vloeistof herwinning is afhanklik van al die veranderlikes wat ondersoek is. Die hoeveelheid ferro-vloeistof wat omtrek is van die ferro-hidrostatiese skeier verminder met 'n toename in die magnetiese veld. Verder is die ferro-vloeistof wat agterbly as gevolg van die feit dat hulle vas is aan die partikels na dreinering, dieselfde as die hoeveelheid wat vasgeheg is aan die die ferro-hidrostatisiese produkte van skeiding by hoë magnetiese velde. Dus is dit belangrik om die ferrohidrostatiese skeier te bedryf by hoë magnetiese velde om sodoende die meerderheid van die ferro-vloeistof in die skeier agter te laat bly. Die hoeveelheid ferro-vloeistof geadsorbeer aan en geabsorbeer deur die partikels verlaag met 'n toename in die materiaal voginhoud. Dit is gevolg van twee redes, nl. eerstens water wat die plek inneem van die oop porieë in die materiaal, en tweede is die feit dat water 'n lagie op die partikeloppervlakte vorm wat ondeurlaatbaar is vir keroseen-basis ferrovloeistof Dit lei tot die vermindering in koste van die ferro-hidrostatiese skeidingstegnologie wanneer nat materiaal in plaas van droë materiaal gebruik word. Soos alreeds genoem, partikels groter as 2.8 mm kan nat behandel word sonder enige negatiewe effekte op die skeiding. Vir -8+4 mm partikels is daar 'n ferro-vloeistofverlies van 0.6 tot 0.14 kg/ton voer vir' n 0-10% voginhoud. Die hoeveelheid ferro-vloeistof per ton voer materiaal wat verlore gaan wissel tussen 0.73 tot 0.56 kg vir -0.85+0.5 mm tot -12+8 mm partikelgroottes, respektiewelik. Die toename in ferro-vloeistofverlies by kleiner partikels is as gevolg van die toename in die oppervlakarea van kleinpartikels vir ferro-vloeistof adsorpsie. Daar is 'n toename in porositeit wat gepaard gaan met 'n toename in hoeveelheid in ferro-vloeistof wat verlore gaan as gevolg van probleme met die herwinning van ferro-vloeistof wat binne-in partikelporieë vasgevang IS. Die byvoeging van water by groter materiaal verlaag die hoeveelheid . ferro-vloeistofwat verlore gaan as gevolg van verminderde porositeit. Die modellering van die hoeveelheid ferro-vloeistof wat verlore gaan, as 'n funksie van die partikelgrootte en porositeit, sal help met die skatting van die hoeveelheid ferro-vloeistof benodig om 'n sekere hoeveelheid materiaal te behandel. Dit is gevind dat die kwaliteit van die ferro-vloeistof wat herwin word dieselfde is as die wat aanvanklik gebruik is vir die materiaal skeiding. Dit wys dat die skeidingseffektiwiteit beïnvloed nie die gebruik van gehersirkuleerde ferro-vloeistof nie.

The channel flow method has established the net dissolution kinetics of calcite single crystals at high pH (7.7-9.7) and varying bulk Ca²⁺ concentrations (0-10 mM), using wide ranges of solution flow rates (10^-3-0.3 cm³ s^-1). Literature rate equations were in poor agreement with experiment. Modelling with the following mechanism, where Ca²⁺ and CO₃^2- undergo Langmuirian adsorption: Ca²⁺_(aq) ⇄ Ca²⁺_(ads) CO^2-3 (aq) ⇄ CO^2-_{3 (ads)} Ca(sup>2+(ads) + CO^2-_{3 (ads)} ⇄ CaCO_{3 (ads)} CaCo_{3 (ads)} → CaCo_{3 (lattice)} and the consequent rate law J_net/mol cm^{-2s-1 = k_pK_CaK_CO3 {K_sp - [Ca2+]_o[CO2-₃]_o (1 + K_Ca[Ca2+]_o)(1 + K_{CO3[CO2-3]o) gave excellent agreement with experiment under all conditions studied. This mechanism is shown to explain all literature streaming potential, electrophoresis and kinetic salt effect data. Dissolution of calcite under the above conditions was strongly inhibited by Mg2+ and fully deprotonated forms of succinic acid, 2-sulphobutanedioic acid, phthalic acid and maleic acid. Mechanisms were established; for the maleate dianion, the inhibition was due to the blocking of the dissolution sites at which CaCO3 units are incorporated into the crystal lattice. For the other ions, inhibition arose from competitive Langmuirian adsorption either between CO32- and the anions, or between Ca2+ and Mg2+. A new method to quantify the inhibited dissolution of particulate CaCO3 (=10 μm) via enhanced mass transport of solution to the rotating disc electrode, due to the rotation of the particles in the diffusion layer, has been established. Good agreement was found with that measured independently using the channel flow cell. A.c. impedance spectroscopy has been used to characterise scaled (CaCO3) steel tubes. Results provide scope for (i) monitoring scale growth, and (ii) use in safety control devices for alerting to the scaling of pipe-work.}}

Computer aided molecular design (CAMD) is a powerful technique to design molecules or chemical mixtures that fulfil a set of desirable target properties as specified by users. Molecular physical and thermodynamic properties are selected as the target properties to ensure that the designed molecules can achieve the property functionalities. However, the aspects of safety and health are not strongly emphasised as design objectives in many CAMD problems. In order to ensure that the synthesised molecule does not cause much harm and health-related risks to the consumers, it is critical to integrate both safety and health aspects as design factors in the current CAMD approaches. The main focus of this research is to develop a novel chemical product design methodology that integrates the concept of inherent safety and occupational health aspects in a CAMD framework. The generated molecules that are optimised with respect to the target properties must be evaluated in terms of their safety and health performance. The assessment is conducted by safety and health-related parameters/sub-indexes that have significant adverse impact on both aspects. This proposed approach ensures that a product that possesses the desirable properties, and at the same time meets the safety and health criteria, is produced. The next focus of this research is to generate optimal molecules with the desired functionalities and favourable safety and health attributes in a single-stage CAMD framework. Besides target properties, the concept of inherent safety and health is also considered as design objective to ensure that the synthesised molecules are simultaneously optimised with regards to both criteria. Fuzzy optimisation approach is applied to optimise these two principal design criteria in this work. As molecular properties are utilised as the parameters to examine the safety and health features of the molecules, these properties are often estimated through property prediction models. This research also focuses on the management of uncertainty resulted from properties used in the sub-indexes. The quantification of uncertainty helps to revise the safety and health measurement so that it can better reflect the inherent hazard level of the molecules. The fourth focus of this research is to address the limitations present in the current method of molecular hazard quantification. The enhancement is carried out by adopting the ordered weighted averaging (OWA) operator method with the analytic hierarchy process (AHP) approach in the safety and health assessment. Two case studies on solvent design are considered to demonstrate the presented methodologies.

Trois dérivés d'amino acides sont reconnus d'une manière stéréo sélective par l'albumine du sérum bovin. Cette propriété a été observée dans le cas de la phosphatase alcaline de tissu non spécifique, (TNAP). Des inhibiteurs agissant à trois niveaux distincts sur les processus de minéralisation ont été cherchés: 1) TNAP ; 2) Formation de l'hydroxyapatite (HA); 3) Vésicules maticielles (VMs). Nous avons trouvé que des dérivés de benzothiophènes et de tétramisoles, solubles dans l'eau, sont des inhibiteurs spécifiques de TNAP. Un modèle qui permet de produire du HA, a été développé et a confirmé que les nucléotides sont des inhibiteurs de formation de HA. Nous avons montré que le médicament anti-rhumatisme sinomenine, n'ayant aucun effet sur le TNAP, ainsi que la théophylline ralentissaient tous les deux la formation de HA induits par les VMs. Ces modèles de minéralisation présentent un grand potentiel lors du criblage de médicaments pour le traitement de l'ostéoarthrose

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
A cinética da carbocloração do pentóxido de vanádio (V2O5) puro, pelo tratamento com gás cloro, de misturas sob a forma de pó, não-compactadas, de V2O5 e grafite (agente redutor), foi investigada, com o emprego do método termogravimétrico, no intervalo de 350 a 550°C, sendo estudada a influência, sobre a velocidade de reação, das seguintes variáveis: temperatura de cloração, percentagem de agente redutor na amostra inicial e pressão parcial do cloro. Na avaliação do efeito da temperatura de cloração sobre a cinética da reação, o Modelo do Núcleo Não Reagido foi utilizado para interpretar os resultados experimentais obtidos. O valor calculado para a energia de ativação da reação foi de 52 kJ, na faixa de 350 a 400°C, sugerindo a reação química como a etapa controladora do processo, e de 12 kJ, na faixa de 400 a 550°C, caso em que a difusão do gás reagente (condições fluidodinâmicas) poderia ser o mecanismo controlador. O efeito da percentagem de carbono, no intervalo de 17 a 30%, nas temperaturas de 350 e 500°C, revelou comportamentos distintos da reação, sugerindo a predominância, conforme o caso estudado, de fatores diferentes, tais como o contato sólido-sólido, atuando para aumentar a taxa de reação, e o excesso estequiométrico de carbono ou a dificuldade de penetração do gás reagente, concorrendo para diminuir a taxa de reação. A reação investigada caracterizou-se por ser aproximadamente de segunda ordem em relação ao cloro, à temperatura de 350°C, e, de primeira ordem, a 500°C.
The kinetics of the carbochlorination of pure vanadium pentoxide (V2O5) by the treatment of a powdered mixture of V2O5 and graphite with chlorine gas, was investigated, using the termogravimetric method, in the temperature range of 350°C to 550°C. The effect of chlorination temperature, amount of reducing agent (graphite) and partial pressure of chlorine gas on the reation kinetics was studied. Regarding the influence of temperature on the reaction kinetics, the shrinking-core or topochemical model was used to explain the experimental results obtained during this study. The activation energy of the reaction, in the temperature range of 350 to 400°C, was 52 kJ, suggesting the chemical reaction as the rate controlling step, and, in the temperature range of 400 to 550°C, was 11 kJ, as the diffusion of the reacting gas (fluid-dynamic conditions) seems to be the limiting step. The effect of the amount of graphite, in the range of 17 to 30%, at the temperatures of 350°C and 500°C, leads to distinct reaction behaviors, distinguishing the predominance of different factors according to the case studied, such as the contact between the reacting solids, which acts in order to increase the reaction rate, and the excess of carbon amount or the difficult of penetration of the reacting gas, acting towards a reduction of the reaction rate. The reaction occurred to be about second-order with respect to Cl2, at the temperature of 350°C, and first-order, at 500°C.